1. Field of the Invention
The present invention relates to packaging stress mitigation for semiconductor dies, and more particularly to packaging stress mitigation for MEMS dies such as in MEMS pressure sensors.
2. Description of Related Art
A variety of devices are known in the art for isolating semiconductor dies from packaging stress and the like. Packaging stress is the stress imparted on a semiconductor die by the package to which it is mounted. This can arise due to the semiconductor die having a different coefficient of thermal expansion from the packaging to which it is mounted and/or from the adhesive mounting the die to the package. In such cases, a change in temperature can cause a stress/strain on the semiconductor die, and depending on the function of the die, this stress/strain can impair performance. Packaging stress can also be caused by mechanical mounting stress from how the die is mounted in the package and how the package itself is mounted in its surroundings.
In one example of packaging stress, traditional piezo resistive MEMS pressure sensors are designed to sense the stress on a diaphragm due to an applied pressure. It is therefore important that the only stress that the piezo resistors experience is due to the applied pressure and not to packaging stress. In such sensor packages, for example where a semiconductor MEMS die is directly mounted to a metallic package, there can be significant packaging stress due to mechanical mounting stress and thermal expansion stress as explained above. Such traditional sensor packages can be made at a relatively low cost, but the packaging stress on the diaphragm makes pressure measurement problematic in terms of accuracy.
Some measures have been taken to address these problems associated with packaging stress. For example, in some traditional MEMS pressure sensor packages, packaging stress mitigation was achieved by thickening the topping and backing wafers enclosing the diaphragm, adding a pedestal made of Pyrex® (available from Corning Incorporated of Corning, N.Y.) between the package and MEMS die, and using a large, custom package to house it all. These measures have been found to provided ten times increase of accuracy in pressure measurements made with the sensor packages so configured. However, the stress mitigation features add to the cost and size of the sensor packages.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for systems and methods of mitigating packaging stress. There also remains a need in the art for such systems and methods that are easy to make and use. The present invention provides a solution for these problems.